Traveling wave particle separator including a rectangular waveguide lined with a dielectric material

ABSTRACT

A tunable RF power source is connected to a particle deflecting structure comprising a waveguide mounted to pass a particle beam therethrough and lined with a dielectric material for reducing the phase velocity of electromagnetic waves within the waveguide. The frequency of the RF source is tuned so that the phase velocity of the electromagnetic waves propagating in the waveguide equals the velocity of desired particles in the particle beam. During passage of the particle beam through the waveguide the electromagnetic waves continuously interact with the beam, but only the desired particles receive a net deflection relative to the other particles in the beam.

United" States Patent [72] inventors John W. Dawson Clarendon Hills;

Robert L. Kustom, Oak Lawn, both of Ill.

[21] Appl. No. 838,433

[22] Filed July 2, 1969 [4'51 Patented Sept. 28, 1971 [73] Assignee The United States of America as represented by the United States Atomic Energy Commission [54] TRAVELING WAVE PARTICLE SEPARATOR INCLUDING A RECTANGULAR WAVEGUIDE LINED WITH A DIELECTRIC MATERIAL 5 Claims, 4 Drawing Figs.

[52] US. Cl 250/413 DS, 250/419 TE [51] Int. Cl. l-I0lj 39/36 [50] Field of Search 250/419 DS, 41.9 TF

[56] References Cited UNITED STATES PATENTS 3,093,733 6/1963 Blewett et al. 250/419 DS 3,278,745 10/1966 Loew 260/4l.9DS

3,452,191 6/1969 Hahn et al. 260/419 DS OTHER REFERENCES A. F. Harvey; Microwave Engineering; Academic Press lnc., New York; (1963); pp. 27- 30 Primary Examiner-Anthony L. Birch Attorney-Roland A. Anderson ABSTRACT: A tunable RF power source is connected to a particle deflecting structure comprising a waveguide mounted to pass a particle beam therethrough and lined with a dielectric material for reducing the phase velocity of electromagnetic waves withih the waveguide. The frequency of the RF source is tuned so that the phase velocity of the electromagnetic waves propagating in the waveguide equals the velocity of desired particles in the particle beam. During passage of the particle beam through the waveguide the electromagnetic waves continuously interact with the beam, but only the desired particles receive a net deflection relative to the other particles in the beam.

l TRAVELING WAVEPARTICLE SEPARAIOR INCLUDING A RECTANGULAR WAVEGUIDE LINED WITH A DIELECTRIC MATERIAL CONTRACTUAL ORIGIN OF THE INVENTION The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

BACKGROUND OF THE INVENTION The present invention relates to devices for separating desired particles in a beam of particles and particularly to a particle separating device in which desired particles are separated by subjecting the beam of particles to transverse forces generated by propagating electromagnetic fields.

Presently, particle separators employ either electrostatic or radiofrequency point deflecting structures to effect separation of desired particles in a beam of particles passing between the deflecting structures.

Particle separators with electrostatic structures are generally useful only withparticles having relatively low momenta, such as up to 5.5 GeV/C for kaons and 8.5 GeV/C for antiprotons. At higher momenta, electrostatic separation of particles encounters very difiicult practical problems, as is well known in the art. For particles with these higher momenta, separators with two or three radiofrequency deflecting structures are used which essentially act on the particle beam as point deflecting sources. Among the disadvantages of such a multistructure separator are the fact that it operates only at discrete particle momenta unless one deflecting structure is made movable. Also, multistructure separators employ several power amplifiers and modulators and require strict tolerances on modulator ripple and temperature control.

It is therefore an object of the present invention to provide a particle separating device employing a single deflectingstructure.

It is another object of the present invention to provide a particle separating device capable of separating particles over a continuous band of momentum by changing the operating frequency of the device.

It is still another object of the present invention to provide a 1 particle separating device in which a single waveguide structure supports traveling electromagnetic waves interacting with a particle beam passing through the waveguide structure to effect continuous deflection of desired particles in the beam.

SUMMARY OF THE INVENTION The device includes an RF power source and a dielectric- Ioaded waveguide structure receiving the output of the RF source for subjecting a beam of relativistic particles passing through the waveguide to transverse deflecting forces generated by propagating electromagnetic fields in the waveguide to effect separation of desired particles in the beam.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 illustrates a waveguide receiving a beam of relativistic particles and supporting a traveling electrmagnetic wave;

FIG. 2 illustrates the positions of certain beam particles in the waveguide of FIG. 1 relative to the phase of the electromagnetic wave in a frame of reference moving at the phase velocity of the electromagnetic wave;

FIG. 3 illustrates the principal components of the preferred embodiment of the present invention; and

FIG. 4 is a perspective view of the waveguide of FIG. 3 and illustrates the coordinate system used in the mathematical description of the modes supported by the waveguide 20.

PREFERRED EMBODIMENT OF THE INVENTION Proper understanding of the present invention is aided by first considering certain basic aspects of the interaction between a traveling electromagnetic wave and a beam of relativistic particles within a waveguide.

Referring to FIG. I, there is shown a waveguide 2 receiving along its longitudinal axis a collimated beam 4 of particles having the same momentum and different rest masses, and an RF source 6 connected to the waveguide 2 in order to produce therein a traveling electromagnetic wave 7. Within the waveguide 2 the traveling electromagnetic wave 7 generates forces which are transverse to the longitudinal axis of the I waveguide. With the beam 4 containing relativistic particles l2, l4 and 16, having different velocities V V I4, and 1616, respectively, and the phase velocity V, of the traveling electromagnetic wave equal to V only particles I4 entering the waveguide 2 at a favorable phase angle undergo continuous unidirectional transverse deflection from the forces generated by the electromagnetic wave 7 while in the waveguide 2. Other particles in the beam 4 leave the waveguide 2 with little or no net deflection.

Referring to FIG. 2, the effect of the traveling electromagnetic wave 7 on the beam 4 within the waveguide 2 of- FIG. I may be more clearly understood by viewing the particles l2, l4, and 16 relative to the phase of the traveling electromagnetic wave in a frame of reference moving with velocity V The particles 14 when entering the waveguide 2 at a favorable phase angle, i.e., other than during the zero axis crossing or polarity reversal of the electromagnetic wave 7, will be subject to the transverse forces generated by the electromagnetic wave 7 and illustrated by the force vectors I7. However, since the velocity of the particles I4 and the phase velocity of the electromagnetic wave 7 are equal, the forces acting upon the particles 14 will be constant and unidirectional throughout the length of the waveguide 2 through which the particles travel. The particles 14 thereby receive a net unidirectional transverse deflection while passing through the waveguide 2. The forces on particles 14 entering the waveguide 2 at a time when the electromagnetic wave 7 reverses polarity have zero magnitude and such particles receive no deflection while passing through the waveguide 2.

Particles l2 and 16 having velocities different from V tend to slip forward or backward in the phase of the electromagnetic wave. With the length of the waveguide 2 being chosen such that the particles 12 and 16 experience a change of at least 3/21r radians of the phase of the electromagnetic wave 7, particles 12 and 16 during their passage through the waveguide 2 will thus undergo little or no net deflection from the transverse forces generated by electromagnetic wave 7.

Referring now to FIG. 3 the preferred embodiment of the present invention for separating desired particles from a particle beam includes a waveguide 20 of rectangular cross section and predetermined length and a stopping block 30 disposed at one end of the waveguide 20. A tunable RF source 40, such as a klystron, is connected to the waveguide 20 via a coupling means 42 to produce therein electromagnetic waves propagating in the direction of the stopping block 30. A frequency meter 44 is connected to the RF source 40 to monitor the output thereof. The other end of the waveguide 20 is connected via a suitable transition means 51 to a particle beam tube 50 which supplies parallel to the longitudinal waveguide axis a collimated beam of relativistic particles 52 having 5 the same momentum. The stopping block 30 is sized and positioned along the waveguide axis so as toabsorb the particle beam 52 exiting from waveguide 20 along the same axial path as it entered the waveguide. Particles deflected from the beam 52 under the influence of the transverse forces generated by the propagating electromagnetic waves in the waveguide 20 pass through the space 32 between the stopping block 30 and the waveguide. Means, not shown, are provided to operate the beam tube 50 and the waveguide 20 in a vacuum.

In the waveguide a pair of opposite walls 22 and 24 are each lined with a low loss dielectric layer 26 and 28, respectively, such as aluminum oxide or beryllium oxide. The dielectric linings 26 and 28 cause a rearrangement of the field distribution or modes associated with the propagating electromagnetic waves in the waveguide 20. In these modes supported by the dielectric line waveguide 20 electromagnetic waves with phase velocities less than the speed of light generate transverse forces which act on the particle beam. Furthermore, by varying the output frequency of the tunable RF source 40 the phase velocity of the electromagnetic waves acting on the particle beam is varied over a wide range of velocities, allowing separation of particles in the beam over a continuous band of particle momenta.

In particular, the dielectric lined waveguide 20 can support either one of two linearly independent modes, both of which generate suitable transverse forces for separating desired particles in the beam 52. The first of these two independent modes have no electric field perpendicular to the dielectric linings of the waveguide 20 and are called the longitudinalsection electric modes. The second of these two independent modes have no magnetic field perpendicular to the dielectric lining of the waveguide 20 and are called the longitudinal-section magnetic modes.

A mathematical description of these two independent modes is as follows:

As shown in FIG. 4, a rectangular XYZ coordinate system is positioned at the beam entrance to the waveguide 20 of F IG. 3 with the X-axis parallel to the walls 22 and 24 and perpendicular to the longitudinal axis of the waveguide, with the Y-axis perpendicular to the walls 22 and 24, and with the Z-axis parallel to the longitudinal axis of the waveguide. Let s, the permittivity of the dielectric linings 26 and 28, 7= thickness of the dielectric linings 26 and 28, I the distance of the walls 22 and 24 respectively above and below the X-axis, and s width of the waveguide 20.

The components of the longitudinal-section electric modes are given by E=jw;.t v 1r y where 1th is the Hertzian potential and S111 a sinh -y,,Y

The transverse deflecting force generated by the longitudinalsection electric modes is proportional to the H field component of these modes.

The field components of the longitudinal-section magnetic modes are given by =j o (y) my In the longitudinal-section magnetic modes the generated transverse deflecting force on a desired particle traveling with velocity V is proportional to (E,,V,B,).

Before operation of the device, the output frequency of the RF source 40 in FIG. 2 is increased from a minimum value until propagation of electromagnetic waves takes place in the waveguide 20, i.e., the cutoff frequency of the first dominant mode. In the present embodiment the longitudinal section magnetic mode appears first. The longitudinal section electric mode appears at higher output frequencies of the RF source 40. The velocity associated with desired particles in the beam are determined and the frequency output of the RF source 40 is further increased to produce the aforedescribed electromagnetic waves with phase velocities equal to the velocity of the desired particles.

In operation of the device, and with a collimated particle beam 52 entering the waveguide 20, transverse forces generated by the particular electromagnetic waves of a mode supported by the wave guide at the selected operating frequency continuously deflect particles in the beam 52. Only the desired particles entering the waveguide at a favorable phase angle and having velocities equal to the phase velocity of the generated electromagnetic waves receive a net displacement with respect to the beam of particles allowing their passage through the space 32. All other particles in the beam 52 are absorbed by the stopping block 30.

Although the device has been described with two dielectric linings along opposite walls, it has been observed that the device operates also with a single dielectric lining placed along either wall 22 or 24 of the rectangular waveguide 20.

Since by the present invention desired particles are separated according to particle velocity, the device of FIG. 3 operates, of course, equally well for extracting particles with the same velocity from a beam of particles having different momenta.

Persons skilled in the art will, of course, readily adapt the general teachings of the invention to embodiments other than the specific embodiment illustrated. Accordingly, the scope of the protection afforded the invention should not be limited to the particular embodiment shown in the drawings and described above, but shall be determined only in accordance with the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A device for separating desired particles from undesired particles in a particle beam, comprising:

waveguide means of predetermined length and rectangular in cross section mounted to pass said particle beam therethrough;

dielectric means disposed within said waveguide means along the length thereof; and

a tunable source of RF energy connected to said waveguide means for propagating therethrough electromagnetic waves with a phase velocity equal to the velocity of said desired particles to effect their separation from said particle beam.

2. The device according to claim I wherein the length of said waveguide means is such that said undesired particles experience a change of RF phase of at least 3/211.

3. The device according to claim 1 wherein said dielectric means comprises a first and second layer of dielectric material respectively deposited on each of pair of opposite walls of said waveguide and along the length thereof.

4. The device according to claim 3 wherein said dielectric material comprises aluminum oxide.

5. A device for separating desired particles from a beam of particles having different momenta, comprising:

a waveguide of rectangular cross section and of predetermined length mounted to pass said particle beam therethrough;

absorbing said particle beam after passage thereof 5 through said waveguide; and

a tunable source of RF energy connected to said waveguide for propagating therethrough electromagnetic waves with a phase velocity equal to the velocity of said desired particles to effect their separation from said particle beam. 

1. A device for separating desired particles from undesired particles in a particle beam, comprising: waveguide means of predetermined length and rectangular in cross section mounted to pass said particle beam therethrough; dielectric means disposed within said waveguide means along the length thereof; and a tunable source of RF energy connected to said waveguide means for propagating therethrough electromagnetic waves with a phase velocity equal to the velocity of said desired particles to effect their separation from said particle beam.
 2. The device according to claim 1 wherein the length of said waveguide means is such that said undesired particles experience a change of RF phase of at least 3/2 pi .
 3. The device according to claim 1 wherein said dielectric means comprises a first and second layer of dielectric material respectively deposited on each of pair of opposite walls of said waveguide and along the length thereof.
 4. The device according to claim 3 wherein said dielectric material comprises aluminum oxide.
 5. A device for separating desired particles from a beam of particles having different momenta, comprising: a waveguide of rectangular cross section and of predetermined length mounted to pass said particle beam therethrough; first and second layers of dielectric material respectively deposited on each of a pair of opposite walls of said waveguide and along the length thereof; a stopping block disposed at one end of said waveguide for absorbing said particle beam after passage thereof through said waveguide; and a tunable source of RF energy connected to said waveguide for propagating therethrough electromagnetic waves with a phase velocity equal to the velocity of said desired particleS to effect their separation from said particle beam. 